1. Field of the Invention
This invention relates to a thin film magnetic head formed on a substrate having top and bottom pole pieces, coil windings and a superstrate, and more particularily relates to a thin film magnetic tape head assembly which includes an insulating structure having a thin gap defining portion for establishing the thickness of a transducing gap between the top pole piece and bottom pole and a thick coil windings enclosing portion which encapsulates that portion of the coil windings located on the bottom pole piece. A leveler layer is formed on the top pole piece, and a superstrate is placed onto the leveler layer to enclose the contoured outer surface of the top pole piece. The thin film magnetic tape head assembly defines a tape engaging surface that is highly resistent to being abraded by a magnetic tape being moved thereacross. A method for forming the leveler layer and affixing the superstrate thereto is disclosed.
2. Description of the Prior Art.
It is well known in the art to form a thin film magnetic head on a substrate wherein the magnetic head comprises a substrate, top and bottom pole pieces, a coil having multiple windings which may be stacked or located between the pole pieces. A typical thin film head of this structure is illustrated in FIG. 1. of the drawing, and is labeled as "Prior Art". In FIG. 1, the substrate 30 has a deposited bottom pole piece 32 which is relatively planar in shape, and one end thereof, front gap section 34, which defines one side of a transducing gap 40. A deposited planarized coil having a plurality of coil windings, shown generally as 42, is encapsulated in an insulating layer 44. A portion of the insulating layer 44 defines the thickness of the transducing gap 40. A deposited top pole piece 46 located on the insulating layer 44 has a front gap section 48 that defines the other side of the transducing gap 40 and the other end is contiguous the rearwardly extending portion of the bottom pole piece to form a rear magnetic closure section 49. An overcoat layer 50, formed of a material that will conform to the contoured stepped outer surface 52, is deposited on the top pole piece 46. An adhesive or filler layer 58 is then applied over the overcoat layer 50 to form a relatively planar surface for supporting a superstrate 59. A magnetic tape, shown as tape 54, is transported across the thin film magnetic head to coact with the magnetic pole pieces 32 and 46 and the transducing gap 40.
EPO Publication No. 0 051 123 discloses a magnetic transducer having top and bottom substrates formed of a magnetic material, which function as the pole piece, with a deposited thin film coil between the pole pieces.
In another known prior art, a ferrite magnetic head illustrated in FIG. 2, has a thick magnetic pole piece 60, formed of a ferrite material, which has a slot 62 formed therein and which is filled with a glass material 64. The glass material 64 placed in the slot 62 functions to receive and support a spiral coil having coil windings 66, which are, in turn, encapsulated in an insulating structure 74. The combination of the slot, glass and coil windings function to physically impose a separation between the pole pieces. As shown in FIG. 2, the thick ferrite pole piece 60 has one end 70 thereof defining one side of a transducing gap 72, which gap is filled by an insulating material 68 which is part of an insulating layer 74. A top pole piece 76, which typically is a deposited magnetic layer, has one end thereof, end 78, defining the other side of the transducing gap 72. Also, a rear magnetic closure section 88 is formed rearward of the transducing gap. A protective overcoat layer 80 formed of a material that will conform to the contoured stepped outer surface of the top pole piece 76, is deposited onto the top pole piece 76. An adhesive or filler layer 81 is then applied over the overcoat layer 50 to form a relatively planar surface to receive a superstrate 86. A magnetic tape 84 is transported across the tape engaging surface 86 of the thin film magnetic head.
One specific prior art thin film magnetic head using this structure is disclosed in U.S. Pat. No. 4,490,760 to Kaminaka et al. U.S. Pat. No. 4,490,760 also discloses use of a glass filled slot on the media engaging surface.
A thin film head having a glass filled slot, similar to that disclosed in U.S. Pat. No. 4,490,760, is discussed in an article captioned "High Track Density Thin-Film Tape Heads" which appeared in the IEEE Transactions on Magnetics, Volume Mag-15, No. 3, Jul. 1979 at pages 1130 through 1134, wherein the authors are Kenji Kanai, Nobuyuki Kaminaka, Norimoto Nouchi, Noboru Nomura and Eiichi Hirota (the "Kanai et al. Publication"). In the Kanai et al. Publication, reference is made to FIG. 2 thereof which shows a protective cover placed over a contoured pole piece exposing an area adjacent the transducing portion "A" of the top pole piece. This is referred to as a "large step structure". As noted in the Kanai et al. Publication, a "large step structure" is undesirable.
The Kanai et al. Publication also teaches the concept of a slot being formed in the bottom pole piece, and filling the same with glass. This results in effectively separating the bottom pole piece from the top pole piece. A deposited thin film coil is formed on the glass filled slot. A top pole piece is then deposited onto the thin film coil. This result is a "small step" in the region between the protective layer and the transducing portion "A" of the top magnetic layer. The effect of the "small step" is to reduce the undesirable surface area which forms a portion of the tape engaging surface. This is shown in FIG. 4 of the Kanai et al. Publication.
As is readily apparent from the Prior Art thin film magnetic head assemblies of FIGS. 1 and 2, the magnetic media engaging surface is formed of a plurality of different materials that are subjected to being abraded by the moving magnetic media. It is well known in the art that different materials, when abraded by a magnetic media being transported thereacross, abrade at different rates. In magnetic tape heads, uneven abrading of materials due to a magnetic tape being transported thereacross can result in the formation of grooves at various material boundaries, or otherwise result in the flaking off or smearing of the abraded material along the tape engaging surface.
U.S. Pat. No. 4,422,117 discloses a thin film head having a glass filled slot in the bottom pole piece for supporting a deposited thin film coil. A thin film pole piece is then deposited onto the deposited coil. A superstrate is applied to the contoured top pole piece by means of glass bonding. This results in glass being located on, and forming part of, the tape engaging surface between the superstrate and the contoured top pole piece.
U.S. Pat. No. 4,396,967 discloses a deposited thin film head wherein glass filled slots are formed in a thin ferrite layer affixed to a non-magnetic Barium Titanate Ceramic (BTC) support piece defining one side of a magnetic head structure. A thin ferrite layer is formed on a second BTC support piece which defines the other side of the magnetic head structure. The other BTC support piece has individual coil winding slots formed therein, which, in turn, contain individual coil windings. When the two BTC support pieces are assembled, the glass filled slots mate with the ferrite containing the coil windings in the slot such that the coil windings are enclosed by, and recessed within, the thin ferrite layer. In this structure, the two thin ferrite layers form part of the media engaging surface in the vicinity of the transducing gap.